The present invention relates to an artificial cornea. More particularly, the present invention relates to an artificial cornea used for substituting a cornea of which function has been reduced or lost because of ocular tissue diseases or trauma therefore, thus recovering visual function.
An artificial cornea generally consists of an optical element made of a light-permeable material having good biocompatibility and a skirt for supporting the optical element by fixing on the surface of human ocular tissue or by insertion between the anterior layer and the posterior layer of the cornea. As such an artificial cornea, there are known an artificial cornea having an optical element and a skirt which are integrally molded from the same material, and an artificial cornea obtained by molding these optical element and skirt from different materials and combining them. As materials for such artificial corneas, there are mainly used polymethyl methacrylate, silicone and the like.
However, because biocompatibility of these materials with the surrounding ocular tissues is poor a slight gap is generated between an artificial cornea and the ocular tissue, and bacteria can invade into anterior chamber through the gap to cause suppurative endophthalmitis in some cases. In more severe cases, the implanted artificial cornea is rejected from the ocular tissue because of inflammation.
Recently, an artificial cornea of which a skirt is made of a material having a microporous structure has been approved. As an example of the artificial cornea of which the skirt is made of a material having a microporous structure, there is known an artificial cornea consisting of an optical element made of a visible light-permeable transparent plastic material and a skirt made of a flexible porous fluorocarbon polymer (Japanese Unexamined Patent Publication No. 158859/1992).
However, since such an artificial cornea has simply the skirt made of a flexible porous fluorocarbon polymer having the microporous structure, it is difficult to prevent leakage of aqueous humor and invasion of bacteria.
In addition, recently an artificial cornea has been proposed which has a skirt made of a hard material such as metal. However, this artificial cornea has such drawbacks that it is extremely difficult to suture the skirt with a suturing needle, that aqueous humor is lost to cause the operation to fail, and that because a metallic skirt is hard, poor in flexibility and shows high stress for the cornea, a part of the skirt is externally exposed by rupture of cornea within a short period of time after implantation into ocular tissue and bacteria can invade into the anterior chamber through the ruptured part to cause suppurative endophthalmitis. Further, such artificial cornea has such drawbacks that corneal tissue is necrosed resulting in extrusion of the artificial cornea, and that fixation is relaxed by an external force generated between the artificial cornea and eyelid resulting in extrusion of the artificial cornea.
In addition, among conventional artificial corneas, there are artificial corneas having a hole for a suture in the skirt in order to fix the artificial cornea. However, such artificial corneas have problems upon elevation of intraocular pressure, namely loss of aqueous humor and invasion of bacteria through the hole, and poor compatibility with the surrounding ocular tissue.
Then, the present inventors intensively studied to solve the above problems and achieved an artificial cornea by which problems such as compatibility with ocular tissue, leakage of intraocular aqueous humor, intraocular invasion of bacteria and stimulation on palpebral conjunctiva have been solved (Japanese Unexamined Patent Publication No. 182762/1997). As shown in FIG. 8, such an artificial cornea comprises an optical element 2 and a skirt 3 having a microporous structure, and a non-water-permeable layer 5 is provided on the surface thereof, so that invasion of bacteria from the external environment can be prevented and leakage of aqueous humor can be prevented. In addition, when the artificial cornea 10 is implanted, cells grow into the micropores of the skirt 3 from corneal tissue 6, resulting in firm binding between the artificial cornea 10 and the corneal tissue 6.
In this way, such an artificial cornea is an excellent one which has solved various conventional problems and has high availability. The present invention has been accomplished in order to further improve such an artificial cornea.
In the meanwhile, as shown in FIG. 9, cell growth occurs inherently at a wound such as an incisional wound and the wound subsequently heals. Upon this occurring, at a wounded part on cornea in contact with an artificial cornea, cells 11 grown from the corneal tissue 6 occasionally grow from the incisional wound surface facing the skirt 3 toward the posterior surface 12 of the artificial cornea 10 (side facing an anterior chamber). This phenomenon is referred to as xe2x80x9cdown growthxe2x80x9d. It is thought that this down growth is caused mainly because the restoring function of corneal epithelial cells at the incisional wound surface recognizes the artificial cornea 10 as a foreign body, so that the epithelial cells 11 do not migrate at the front surface 13 of the artificial cornea 10.
However, as the the time elapses after implantation, the down growth gradually progresses as shown in FIG. 9. Accordingly, it was found that, when the grown cells 11 initiate to cover the posterior surface of the optical element 2, not only is excellent transparency of the optical element 2 not fully maintained, but also the artificial cornea 10 is forwardly (extraocularlly) put and excluded from the corneal tissue 6 possibly resulting in extrusion of the artificial cornea even if the corneal tissue 6 and the artificial cornea 10 firmly adhere to each other due to the microporous structure in the skirt 3 as in the above invention.
The present invention has been accomplished in view of the above prior work, and aims at providing an artificial cornea which is well compatible with ocular tissue, which prevents leakage of intraocular aqueous humor and intraocular invasion of bacteria, reduces stimulation on palpebral conjunctiva and further inhibits progression of down growth, and which has no possibility of reduction in transparency of the optical element due to down growth as well as detachment and extrusion from the host cornea in the implanted state.
The present invention relates to an artificial cornea comprising an optical element made of an optically transparent material, having a front surface and a posterior surface, and a skirt provided so as to support with surrounding at least a part of the optical element, characterized in that the skirt is provided with a flange on its side facing the interior of eyes during implantation of the artificial cornea, and the flange radially protrudes outward from the skirt.